The ancient art of laying rope
DTU Nanotech, Building 345 East, Ørsteds Plads, Technical University of Denmark 2800 Kongens Lyngby, Denmark
Accepted: 21 February 2011
We describe a geometrical property of helical structures and show how it accounts for the early art of rope-making. Helices have a maximum number of rotations that can be added to them —and it is shown that this is a geometrical feature, not a material property. This geometrical insight explains why nearly identically appearing ropes can be made from very different materials and it is also the reason behind the unyielding nature of ropes. Maximally rotated strands behave as zero-twist structures. Hence, under strain they neither rotate in one direction nor in the other. The necessity for the rope to be stretched while being laid, known from Egyptian tomb scenes, follows straightforwardly, as does the function of the top, an old tool for laying ropes.
PACS: 01.55.+b – General physics / 02.10.Kn – Knot theory / 07.10.Lw – Balance systems, tensile machines, etc.
© EPLA, 2011